Ultrastructural observations on the male gametes in Austrognathia sp. (Gnathostomulida,Bursovaginoidea)

The male gametes of the gnathostomulid bursovaginoid Austrognathia sp. were investigated by electron microscopy. All stages of sperm development can be observed in the single saccular male gonad, which is enclosed by a relatively thick basement membrane internally reinforced by thin smooth muscle cells. The spermatogonia are situated close to the testicular theca and produce generally separate primary spermatocytes. From secondary spermatocytes onwards, the nuclear envelope is no longer visible. The spermatids develop synchronously in groups of four, in contrast to arthropod and vertebrate spermatogenesis. A single, large nurse cell, or trophocyte, never observed previously, surrounds each spermatid; perhaps it represents an altered germ cell functioning in nutrition. The spermatid nucleus, initially ovoid, lengthens and takes on the shape of a mushroom head extending into a stalk. Three degrees of chromatin condensation are visible. Anteriorly, a palisade-shaped structure is present just over the highly heterochromatic nuclear zone and is considered to have an acrosome-like function. The outer sperm cytoplasm is characterized by a peripheral tubular labyrinth. Axonemal structures have never been found, but centriole-like structures are present among the medium-density chromatinic strands of the mushroom-like nucleus. No cortical microtubules are evident beneath the cell membrane. The external sperm morphology recalls that of nematode gametes, and some internal features are also similar. Phylogenetic considerations and hypotheses on sperm locomotion are proposed. J. Morphol. 237:165–176, 1998. © 1998 Wiley-Liss, Inc.     

Seasonal changes in serum metabolites in free-ranging alpine marmots (<Emphasis Type="Italic">Marmota marmota</Emphasis>)

Circannual changes in serum parameters and body mass were studied in free-ranging Marmota marmota that had been shot in Switzerland (Grisons) for management reasons in May, July, and September of 1995, 1996, and 1997; and in April 1996. Markers of lipid (triglycerides, cholesterol), protein (total protein, urea-nitrogen) and mineral (calcium, inorganic phosphate) metabolism were evaluated in 111 haemolysis-free serum samples; the effects of sex, age, reproductive status, season and year were tested. Mean body mass was higher in adult males than in adult females in July and September, and serum cholesterol concentrations were lower in adult males in May. Pregnant females had lower concentrations of total protein than non-pregnant females, and triglyceride concentrations were negatively correlated with the number of uterine ampullae. Inorganic phosphate decreased and total protein increased with age. In adults, triglycerides, cholesterol and urea-nitrogen increased mainly from May to July and decreased between September and May. Total protein, calcium and phosphate did not change throughout the year. This suggests that, during the active season, ingested lipids and amino acids were utilised for metabolic needs or lipid storage, while in winter, lipids were catabolised and protein was spared. Quantitative differences between years, observed for triglycerides and total protein during the active season, were probably due to different climatic conditions in each year.     

Co-dominant markers for the selection of somatic dihybrids and polyhybrids

Resistance to ouabain and puromycin are shown to represent very useful co-dominant characters for the selection of somatic hybrids between mammalian cells, after fusion with polyethylene glycol. We therefore used, with success, a number of Chinese hamster and mouse cell lines carrying these markers in association with thymidine kinase and hypoxanthine-guanine-phosphoribosyl transferase deficiency for selection of hybrids of triparental origin.     

Different globin messenger RNAs are present before and after the metamorphosis in Lampetra zanandreai

Lampreys are very primitive vertebrates belonging to the Agnata group. Although higher vertebrates have polymeric hemoglobin molecules which are encoded by several differentially expressed genes, lampreys have monomeric hemoglobins. However, it is unclear whether one or more globin genes are present. In this paper we show that four different species of globin can be separated by electrophoresis in acetic acid-urea-Triton gels. Two of the four species are present only before metamorphosis, while the other two are present only during adult life. In order to discover whether these differences are due to post-translational modifications of a unique amino acid sequence, we extracted globin mRNAs from both larval and adult stages and translated them in vitro. We found that both larval and adult globin mRNAs produce single globin bands; however, larval and adult bands are different from each other. Our data are consistent with the idea that two different globin genes are present in lampreys and that they are differentially expressed during development.     

Fish trophic level and the similarity of non-specific larval parasite assemblages

Whereas the effect of parasites on food webs is increasingly recognised and has been extensively measured and modelled, the effect of food webs on the structure of parasite assemblages has not been quantified in a similar way. Here, we apply the concept of decay in community similarity with increasing distance, previously used for parasites in geographical, phylogenetic and ontogenetic contexts, to differences in the trophic level (TL) based on diet composition of fishes. It is proposed as an accurate quantitative method to measure rates of assemblage change as a function of host feeding habits and is applied, to our knowledge for the first time, across host species in marine waters. We focused on a suite of 15 species of trophically-transmitted and non-specific larval helminths across 16 fish species (1783 specimens, six orders, 14 families) with different sizes and TLs, gathered from the same ecosystem. Not all host species harboured the same number and types of parasites, reflecting the differences in their ecological characteristics. Using differences in TL and body length as measurements of size and trophic distances, we found that similarity at both infracommunity and component community levels showed a very clear decay pattern, based on parasite abundance and relative abundance, with increasing distance in TL, but was not related to changes in fish size, with TL thus emerging as the main explanatory factor for similarity of parasite assemblages. Furthermore, the relationships between host TL and assemblage similarity allowed identification of fishes for which the TL was under- or over-estimated and prediction of the TL of host species based on parasite data alone.     

Pauciconfibula patagonensis sp. nov. (Monogenea: Microcotylidae) parasitizing the horsefish, Congiopodus peruvianus (Pisces: Congiopodidae), from the Patagonian Shelf, Argentina

Pauciconfibula patagonensis sp. nov. (Monogenea: Microcotylidae), parasite of gill filaments of the horsefish, Congiopodus peruvianus (Congiopodidae) collected in the Patagonian Shelf, Argentina, is described and illustrated. The new species is characterized by having intestinal caeca not confluent and entering into the haptor, vitelline follicles extending from the genital pore to near the posterior portion of haptor, two parallel rows each comprised of 16-20 microcotylid clamps in the haptor, 25-43 testes and a fusiform egg with one very long tangled polar filament. P. patagonensis is the only member of the genus known to parasitize a scorpaeniform host and represents the first record of a representative of this genus in the southern Atlantic Ocean.     

A new species of Paracapillaria (Nematoda: Capillariidae) parasitizing the Brazilian sandperch, Pinguipes brasilianus (Pisces: Pinguipedidae), from Argentina

A new species, Paracapillaria argentinensis n. sp., is described from the pinguipedid fish Pinguipes brasilianus Cuvier, 1829 from waters off Mar del Plata, Argentina (38 degrees 08'S, 57 degrees 32'W) (prevalence 22.2%; mean intensity +/- SD, 4.42 +/- 5.19). The new species is assigned to the subgenus Paracapillaria Moravec, 1987. Of the 10 species so far known in the subgenus, the new species more closely resembles P. (P.) plectroplites, from which it is distinguished by having a spicule with an expanded anterior end and a slender medial section. A similar spicular morphology is observed in P. (P.) epinephell; however, it shows shorter spicules and a highly reduced caudal bursa. This is the first record of Paracapillaria in the southwestern Atlantic Ocean.